A virus that damages cotton crops has been quietly spreading through U.S. fields for nearly two decades—without anyone noticing.
Scientists once believed the cotton leafroll dwarf virus (CLRDV) arrived in the U.S. only recently.
But new research shows it has been infecting cotton plants as far back as 2006.
The study, published in Plant Disease, was led by researchers from the USDA Agricultural Research Service and Cornell University. Using advanced data-mining tools, the team reexamined old plant samples and public genetic databases to look for signs of CLRDV.
They found evidence of the virus in a 2006 sample from Mississippi, a 2015 sample from Louisiana, and even a 2018 sample from California—years before the virus was officially detected in 2017.
Alejandro Olmedo-Velarde, one of the study’s lead authors, explained that this discovery completely changes the timeline for how the virus spread. Instead of being a new threat, CLRDV has likely been affecting U.S. cotton for years under the radar.
To double-check their findings, the team collected fresh samples from cotton fields in Southern California in 2023. Lab tests confirmed the virus is currently present in the state, marking the first official report of CLRDV in California.
The researchers made these discoveries by analyzing genetic information stored in public databases—materials that were originally collected for other studies. This powerful approach allowed them to spot the virus in samples that no one had tested for CLRDV at the time.
In a surprising twist, the scientists also found traces of the virus in a cow’s gut. This likely came from the cow eating infected cotton plant material in its feed. While the virus does not infect animals, the finding offers new clues about how far the virus may have spread in plants before being officially recognized.
The study also revives interest in a mysterious cotton disease called bronze wilt. Symptoms of bronze wilt have long puzzled scientists, and this new research suggests a possible link to CLRDV.
If true, this could explain crop losses that farmers have faced for years.
According to Dr. Michelle Heck, a USDA scientist involved in the study, the findings are a wake-up call. The virus may be more common than previously thought, and learning how it spread undetected for so long is key to protecting cotton crops in the future.
The research shows how useful old data can be in catching agricultural threats early—and the value of teamwork across scientific fields.
